Pen



FIG. 1 is a front elevation view of a pen showing my new design;

FIG. 2 is a right side elevation view of the pen shown in FIG. 1, with a left side elevation view being a mirror image thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is an enlarged top plan view thereof; and,

FIG. 5 is an enlarged bottom plan view thereof. 

The ornamental design for a pen, as shown and described. 